A driveline of a hybrid vehicle may include and engine and a motor that are selectively coupled together. The engine and motor may be selectively coupled together via a disconnect clutch. The engine and motor may also be coupled to an automatic transmission that includes a torque converter and lockup clutch. The automatic transmission may also include a torque converter and a plurality of fixed gear ratios.
The transmission torque converter lockup clutch may be selectively applied to improve driveline efficiency. The torque converter may also be applied during engine starting while the transmission is in gear to improve vehicle drivability. For example, the lockup clutch may be applied to shape engine speed and an amount of engine torque that is transferred to vehicle wheels or a vehicle chassis when the transmission is in a tied-up state (e.g., when two or more transmission clutches are engaged to couple the transmission input shaft to the transmission case). In particular, the torque converter clutch may be initially open or in controlled slip where little torque converter clutch pressure is applied. As engine speed increases and reaches a desired speed, the torque converter clutch application pressure or force may be increased to improve driveline efficiency. However, if the torque converter application force or pressure is greater than desired during engine run-up or after the engine reaches a desired speed, vehicle drivability and/or emissions may be degraded.
The inventors herein have recognized the above-mentioned issues and have developed a hybrid powertrain operating method, comprising: rotating at least a portion of an electric machine in a driveline; and adjusting operation of a torque converter lockup clutch in response to a current supplied to the electric machine.
By rotating an electric machine and applying a transmission torque converter lockup clutch, it may be possible to improve lockup clutch operation. In particular, it may be possible to accurately determine an amount of torque transferred across a torque converter lockup clutch so that the lockup clutch may be applied with more precision. In one example, an amount of electric current supplied to the electric machine may be a basis for determining the amount of torque transferred across the lockup clutch. During subsequent lockup clutch application, the lockup clutch closing may be scheduled based on a transfer function that was adjusted in response to an amount of torque transferred across the torque converter lockup clutch.
The present description may provide several advantages. Specifically, the approach may improve engine starting by improving engine speed control during engine starting. Further, the approach may reduce lockup clutch wear. Further still, the approach may improve vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.